1. Field of the Invention
The present invention relates to the field of electrical apparatuses comprising microprocessors, and in particular a method and a device reducing their average electrical energy consumption.
2. Discussion of the Background
For certain electrical apparatuses, the need to limit the electrical energy consumption to a minimal value is very great. This is particularly true for public telephone stations. Indeed, the latter are generally supplied via the telephone line and the permitted electrical energy which may be tapped off for operation is very limited.
The problem becomes trickier as public telephone stations are developed further and further.
The document EP 0 275 566 describes a method for reducing the electricity consumption of a public telephone station, in which the control installation comprises a microprocessor. In this method, the frequency of the base cycle of the system, controlled externally, is cut by the microprocessor by means of a cutting signal generated internally at a given instant, and reset later by means of a reset signal generated externally, the reset signal being derived from a control clock whose frequency is low by comparison with the frequency of the base cycle of the system. This method has the following disadvantages:
the system operates at one frequency only, that of the system clock. The control clock merely engages or triggers the clock of the system. During the time which separates such a triggering from the following engagement, the microprocessor is paralysed and is unable to recognize interrupts or external conditions which would normally cause it to react; PA0 the microprocessor cannot handle the time, since the system clock is interrupted intermittently; PA0 it is readily seen that the realizable energy saving cannot exceed 50% in the best of cases.
The document EP-0 391 543 describes a microprocessor clock for a public telephone station, in which a microprocessor peripheral sends an interrupt simultaneously with the speeding up of the clock signal when a data packet is received from the telephone exchange. The interrupt is processed with the aid of the speeded-up clock signal to reduce the response time of the system, which makes it possible to reduce the normal clock frequency so as to save energy. This method has the disadvantage of relying excessively on the microprocessor's peripheral.
In this document it is assumed that the microprocessor is the main consumer of energy and its consumption alone is reduced without tackling that of the peripheral, which may be just as large. The overall consumption of the apparatus is therefore not reduced sufficiently.
Processes are known, for example from European Patent No. 0 155 126, in which an oscillator provides clock pulses required for operating the microprocessor, and in which an expected outside event, or interrupt, as for example the insertion of a coin into the appropriate slot of a public telephone apparatus, prompts a subassembly of the apparatus, namely the system for recognizing and evaluating coins, to pass from the monitoring state to the active state.
However, in these methods, the checking of the electricity consumption of the microprocessor remains rudimentary. During the monitoring state, the microprocessor remains supplied at the normal frequency, which induces still relatively high consumption of electrical energy.